In an accelerator apparatus, which controls acceleration of a vehicle in accordance with an amount of operation on an accelerator pedal by a driver, a rotation angle sensor detects a rotation angle of the pedal. In the rotation angle sensor, plural magnetism detection devices, which rotate relatively to a magnetism generation device provided on a shaft, convert changes in magnetic density into voltages. The accelerator apparatus controls a valve opening angle of a throttle valve in accordance with a rotation angle of the pedal, which is calculated based on the converted voltages. For example, JP 4198544 (patent document) discloses an accelerator apparatus, which is provided with a battery voltage detection device and a sensor power voltage detection device. When power supplied to two magnetism detection devices falls, the accelerator apparatus prevents a throttle valve from being fully closed in response to a fall of the voltages outputted from the magnetism detection devices.
According to the patent document, it is checked whether the accelerator apparatus is operating normally based on a voltage difference calculated from the voltages outputted from the two magnetism detection devices. In an abnormal operation state of the pedal, in which the pedal rotates in an accelerator closing direction exceeding an accelerator full-closure angle corresponding to a full-closure state of the throttle valve, the voltage difference remains within a predetermined range. In this case, the accelerator apparatus is determined to be operating normally. As a result, the rotation angle of the pedal is not determined to be abnormal.